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The Impact of the State of Hydration on the Degree of Hydronephrosis in Children: Towards a Uniform Standard of Ultrasonographic Assessment
Joseph Gleason, M.D.1, Eli Bator, RN2, Paul Bowlin, M.D.2, Walid Farhat, M.D.2, Martin Koyle, M.D.2, Armando Lorenzo, M.D.2, Darius Bagli, M.D.2.
1University of Tennessee and LeBonheur Children's Hospital, Memphis, TN, USA, 2The Hospital for Sick Children, Toronto, ON, Canada.

BACKGROUND: Hydronephrosis is an imaging state that results from integration of a variety of parameters. Changes in the degree of serially assessed hydronephrosis significantly influence clinical management, including indications for surgical intervention and length of follow-up. Currently, no standardized hydration protocol is followed at our institution prior to renal ultrasonography. We hypothesize that the degree of hydronephrosis seen on ultrasound is impacted by the state of relative hydration at the time of the study.METHODS: We prospectively recruited patients aged 6 months to 18 years with known hydronephrosis being seen for follow-up imaging in the Pediatric Urology clinic. Once consent was obtained, the patients were brought to their ultrasound appointments having fasted for ≥4 hours. Upon completion of the initial ultrasound examination, the children were rapidly hydrated orally with 15-20 mL/kg fluid. Breast fed children were simply allowed to drink as much as tolerable. After hydration, a second, more focused ultrasound was performed within 30-60 minutes. The effect of bladder filling was controlled by having toilet trained children void just prior to each study, and by measuring the bladder volume sonographically in all children. The change in hydronephrosis, represented by the antero-posterior diameter (APD) of the renal pelvis, was assessed statistically using a Wilcoxon paired, two-tailed t-test, and significance was determined if p<0.05. The unaffected kidneys studied represented the control group.RESULTS: Twenty-one patients (age 8 months to 16 years), totaling 26 kidneys were included in the analysis, and the unaffected 16 kidneys became the control group. Pre-hydration, the median APD was 8.1 mm (IQR 5-11), and post-hydration was 10.3 mm (IQR 7.5-16). The mean values pre- and post-hydration were 10.5 and 14.2 mm, respectively, with a mean increase of 34.8% following hydration (p<0.001). Also, 8/26 kidneys (30.8%) had an increase of >50%, 13/26 (50%) increased by >25% while 22/26 (84.6%) showed some degree of increase. Additionally, 4/16 (25%) of the control kidneys showed de novo hydronephrosis upon hydration, with a maximum increase to 8 mm dilation of the APD. Bladder volumes were negligible in all studies.CONCLUSIONS: The degree of hydronephrosis is significantly impacted by the state of hydration at the time of the study. A standardized protocol of hydration should be considered when assessing renal dilatation sonographically to avoid over or under estimation of the degree of hydronephrosis.

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